Doorknob



FIG. 1 is a perspective view of a doorknob showing the new design;

FIG. 2 is a front view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a right view thereof;

FIG. 5 is a left view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines represent portions of the doorknob that form no part of the claimed design. 

CLAIM The ornamental design for a doorknob, as shown and described. 